what's inside the several watt laser modules?

[VDX]

... I've put a concave mirror with 50mm FL in front of a 445nm-diode with horizontally oriented fast axis and tested with rotating the mirror, what's the effects to the resulting beam.

Did the same with a diode-bar with 19 emitters in a row and too got promising results ;-)

Viktor

[planters]

I don't understand the details or your set up well enough. It would seem to me that what you describe shouldn't happen, but I don't disbelieve you. I think this shows that exactly what you are doing is not clear.

Yet, I am intrigued.

In general, moderate FL, spherical lenses and mirrors should have the same optical performance. They should both introduce spherical aberration and as the FL drops this should become more and more severe. Off axis comma and astigmatism should also be present with both.

Could you state precisely, item by item, what the arrangement of components is? Maybe, a couple of images would help as well.

[norty303]

Planters, is one factor that you're thinking of a spherical mirror, where I interpretted it as a cylindrical mirror to only correct one axis?

[planters]

Planters, is one factor that you're thinking of a spherical mirror, where I interpretted it as a cylindrical mirror to only correct one axis?

That is one of my thoughts, but I would assume that if he is comparing a mirror to a lens that the comparison would be cylinder vs cylinder or spherical vs spherical. Cross comparing is SO different that the choice of a lens vs a mirror would be overwhelmed.

[norty303]

The thing that got me thinking was the reference to rotating the mirror and how that affected the beam. If it was spherical it would've had no effect at all, but a cylinder would allow you to dial in more or less correction, depending on angle of rotation.

In fact, a mirror like that on the end of a very accurate actuator would allow you to control the divergence in one axis remotely, very quickly if necessary.

[VDX]

... attached some images I've just done freehand with a small concave mirror without any special adjustment.

The first two are with the standard kollimator (G2?)
- the first is the farfield with focus distance maybe 1/4 between the diode and the wall, fast axis oriented horizontal
- second is made with placing the concave mirror some 5 centimeters before the diode with rouglhy 100degs skewing between diode and wall ... bigger angles will 'compress' the mirrored axis even more

- the third image is made with removed lens - 'naked' diode, maybe 1meter distance to the wall
- fourth is the focussing and 'fast' compressing of the beam only with the mirror, no other optics involved - could be much better in homogenity and 'circularity', but this was 'freehand', so a vague shot.

With corresponding mirrors and good justage this could be a perfect aligned round beam with nearly same divergence for fast and slow axes ...

Viktor

[logsquared]

I made a mount years back that bent a mirror for correction of the 445's when they fist hit the streets. Check this thread: http://www.photonlexicon.com/forums/...minimal+optics

My mount only bent in one axis making a cylinder mirror. The thing I learned back then about spherical mirrors is the radius of curvature changes as you move off axis. It's kind of hard to visualize. Think of the handrail on a spiral staircase. If you look at it from the top it has the radius of the stairs. If you look down at an angle away from center the radius appears to be larger.

[blue]

I don't get it...

[planters]

logssquared,
You're right. I remember your posts. That method has been used for maybe more than 100 years to create parabolic reflectors out of plane, flat glass in telescopes. A parabolic reflector decreases its FL with distance from the axis unlike a spherical reflector. A sphere is a sphere and has only one radius, but as your light impinges at an increasing angle to the surface the reflection will be more foreshortened.

VDX,
Thanks for the images. The first two frames have similar vertical spread and so I am now sure that you a using a single axis, cylinder mirror and not a 2 axis, spherical mirror. Right? Here is what I suspect is happening. The mirror added after the collimator is intersecting the beam at a pretty acute angle and so it is acting as an expanding element in the near field, resulting in a decrease in the far field divergence. This is consistent with the fact that as the angle becomes even more acute, the effect is increased. This could be ruled in/out by measuring the near field beam dimensions in each case. Another property of a single axis optic (mirror or lens) is like I said above; you can use it to ALSO correct the astigmatism present after the collimator.

If however, the near field beam does not grow due to this mirror, then you have reveled a significant opportunity to improve laser beams and I want to know as much as possible so I can reproduce this.

[VDX]

The first two frames have similar vertical spread and so I am now sure that you a using a single axis, cylinder mirror and not a 2 axis, spherical mirror. Right?

... no, it's a simple spherical mirror, bought in the 'cosmetic' section of our grocery store ... and I can adjust/morph the beam shape with distance and angle until the complete 'folded' axis forms a vertical line.

I've done this for medium distance focussing with some ten centimeters FL, where the focus is not a small point, but a bar-shape with maybe 0.4x0.1 mm to get it symmetrical again ... and this behaviour can be seen in the far-field too ...

In combination with a collimating/focussing lens this is more complex, so the resulting focus or beam quality depends on the optical characteristics of the diode emitter, and optics parameters ... will try this with some single-mode diodes too, as here it should be more helpfull in relation of lesser losses ;-)

Viktor